Is there anyway so we can create a tablesspace so all objects ( i.e. table/index ) by default created in that tablespace instead of IBM defined tablespace ?

If you are creating objects as instance owner or a user with dbadm, then,afaik, you'll have to explicitly specify the tablespace name or else drop the userspace1 ...

If it is any other user, then reovke use of tablespace userspace1 from that user and grant use of tablespace to the new tablespace you have created ...

HTH

Sathyaram